Showing papers on "Time-division multiplexing published in 1978"

Digital Processing Techniques in the 60 Channel Transmultiplexer

Abstract: Techniques applied to the digital processing of speech and signaling in a 60 channel FDM to 30 channel PCM converter are presented. Great efficiency is achieved through connecting a particular type of Fourier Transform computer to a polyphase network in which coefficient symmetries are exploited. Digital processing parameter values have been chosen so as to meet specified performance objectives. Realization of a laboratory model is outlined and measured performance is reported. Adequacy of the various options retained for the digital processing is confirmed by the experimental results.

A High-Speed FFT Processor

Abstract: A high-speed, low-power, fast Fourier transform (FFT) processor is described in this paper. The FFT processor is designed around parallel arithmetic functions (16 by 16 multiplier and 16-bit adders) and can operate up to a 17.0-MHz clock rate. It performs a 128-point FFT in 250 μs at 16-MHz clock rate and therefore can be used for applications such as frequency-division multiplexing/timedivision multiplexing (FDM/TDM) transmultiplexer. The processor was designed and tested according to the design specifications. Its standalone feature permits its use in a variety of systems employing spectral analysis. The high-speed requirements are met by a real-time address generation scheme. The design can be used for a higher order FFT by providing extra memory space.

Loop carrier system for telecommunication and data services

Abstract: A versatile loop communication system is disclosed wherein recurring frames of the ring carrier signal are divided by a movable partition into a dynamically allocated time division channel portion and a data packet communication portion. A common signal channel, in the ring carrier frame, is used to logically connect and disconnect stations for either circuit or packet communication on a common bus extending from terminals located in the loop. The loop controller automatically forms a contiguous group of time division channels or signal bytes at one end of the ring carrier frame. The format of the time division multiplexing channels is such that dynamic time slot interchanges of signal bytes are produced by the controller without the necessity of counting circuitry in the terminals to identify specific channel locations. The dynamic time slot interchange or byte displacement function is provided by additional memory arrangements both for the signals being transported by the ring and control functions in the time division switch located in the controller. The remaining portion of the frame serves as a shared channel for packet header switched data. In order to provide a flexible basis for packet switching, the controller assigns address tags and retains a map of the system.

Digital TDM-FDM Translator with Multistage Structure

Abstract: In this paper, a new digital signal processing algorithm for the digital TDM-FDM translator is proposed. The digital TDM-FDM translator, which performs a direct translation between two multiplex formats in the telephone network (time-division-multiplexing (TDM) and frequency-division-multiplexing (FDM)) by using digital techniques, has advantages in accuracy and stability of characteristics over equivalent analog equipments. However from the economical point of view, it largely depends on the cost reduction of semiconductor devices and LSI technologies. The proposed algorthm can be realized using only two digital filters and does not require product modulators or Fast Fourier Transform (FFT) processors. The required number of multiplications, which is closely related to the quantity of hardware, is considerably reduced by the multistage structure of this algorithm. The reduction in the kind of required digital hardware and the required number of multiplications makes it possible to efficiently utilize the new hardware realization techniques of digital filters or multipliers using read-only memories and simple logic devices. Since it is foreseen that cost reduction of memory devices will be more rapid than that of logic devices, the proposed algorithm is expected to be advantageous with regard to cost over existing algorithms where complex multiplier logic is required. The estimation of the computation rate is carried out with reference to a practical case. The computer simulation results are also shown.

Hybrid control of time division multiplexing

Abstract: A hybrid multiplexing method and communications system for controlling transmission of information between a plurality of remote terminals and a shared central facility over a common communications channel. The remote terminals are synchronously polled to ascertain whether or not the remote terminals desire access to the central facility. Asynchronous polling is utilized to establish communication between the central unit and the remote terminals desiring access to the central unit.

Development of a TDM/FDM Transmultiplexer

Abstract: Recently, digital systems such as digital telephone switching systems and digital transmission paths are being introduced more and more into communications networks in which signals are handled with Time Division Multiplex (TDM). There still exists, on the other hand, a number of analog transmission paths in which signals are multiplexed with Frequency Division Multiplex (FDM). Therefore, it is important to develop a scheme to interconnect efficiently TDM and FDM systems. Transmultiplexer, which is an equipment directly converting PCM.TDM signals and SSB.FDM signals with each other, is expected to provide an efficient interconneetion between TDM and FDM systems. Authors have developed an experimental transmultiplexer which can provide mutual conversion between a 24-channel PCM primary group (1.544 Mbits/s) and two 12-channel FDM basic groups (60-108 kHz). The developed equipment is designed so as to achieve reduction of the computation rate and simplicity of the hardware by the following techniques: (1) The FFT (Fast Fourier Transform) technique is used to optimize the filtering and multiplexing processes. (2) The spectrum reversion of odd-numbered channel signals is achieved by inverting the sign bits of the PCM signals every other frame. (3) The bandpass sampling technique is applied to obtain SSB.FDM signals directly without frequency shifts at analog FDM stages. In order to evaluate the characteristics of the developed transmultiplexer, experiments have been conducted by connecting it with FDM terminal equipments. The experimental results showed that the transmultiplexer can offer better performance than the tandem connection of standard PCM multiplex equipments and standard FDM terminal equipments with reasonable hardware.

TDM-FDM Conversion Requiring Reduced Computation Complexity

Abstract: We present an approach to perform the conversion between two widely used multiplexing techniques in telephony, time division, multiplex (TDM) to frequency division multiplex (FDM), using digital signal processing techniques. By exploiting some results from the theory of computational complexity we reduce considerably the number of computations required. Furthermore the use of only nonrecursive (FIR) filters whose coefficients are expressed in the canonical signed digit code permits a 16 bit implementation requiring no multiplications and only additions with concurrent shifts which further simplifies the required circuitry.

Design Technique for Multiplexing Asynchronous Digital Video and Audio Signals

Abstract: To apply digital transmission to the distribution of television program material it is necessary to encode both sound and picture signals, protect them from the effects of transmission errors and multiplex them into a form suitable for the transmission link that is to be used. Coding, error protection and multiplexing have all received extensive study but their combined application in a system has received little discussion in the literature. This paper shows how a system was designed for a particular experimental application with a specified total bit rate. Particular emphasis is given to the multiplexing arrangements, including the necessary use of justification techniques. The equipment designed has been used in successful field trials of digital transmission by both cable and satellite.

Switching modulators and demodulators utilizing modified switching signal

Abstract: A switching modulator (FIG. 3) for generating an FM composite stereo signal is disclosed. The modulator includes a switching circuit (40) for time division multiplexing the stereophonically related input signals onto an output line. The operation of the switching circuit is controlled by bilevel switching control signals provided by a function generator (48). The function generator provides bilevel switching control signals which have been modified so that the output of the switching circuit inherently lacks the third harmonic component which would have been present had conventional squarewave switching control signals instead been used. A low-pass filter (56) eliminates other, higher harmonics. A switching demodulator (FIG. 9) is also disclosed. This demodulator demodulates an FM composite signal through use of the same modified switching signal as used in the modulator.

Digital multiplexing and demultiplexing system

Abstract: A digital multiplexing and demultiplexing system for time division multiplexing a number of incoming plesiosynchronous low rate component signals and a number of incoming plesiosynchronous intermediate rate component signals into an outgoing single high rate signal. A first multiplexing stage time stores and stuffs the low rate component signals and multiplexes them into synchronous intermediate rate signals. A second multiplexing stage stores and stuffs the plesiosynchronous and synchronous intermediate rate signals and multiplexes them into the outgoing high rate signal.

A method for increasing the number of majority multiplexed channels

Abstract: A majority multiplexing method for multiplexing some moderately large number of binary data channels is proposed. It is shown that the number of channels can be increased if the transmitted signal is formed by using a two-stage transformation process. A suitable detection process for recovering the binary data elements is established. Results of computer studies on the performance of the method in additive white Gaussian noise are presented, and the method is briefly compared with TDM.

Transmission system for control signal of key telephone set

Abstract: PURPOSE:To obtain a key telephone set using the simple time division multiple signal transmission system adapted for transmission of a medium distance, by displaying the synchronizing signal by the absence of a clock signal and by enlarging the amplitude of a control signal more than that of the clock signal. CONSTITUTION:A clock signal (a) and a synchronizing signal (b) are supplied from a generating circuit 18 to a parallel-serial converting circuit 11 and a down signal transmitting circuit 12, and a control signal (c) subjected to time division multiplexing by the converting circuit 11 is transmitted from the down signal transmitting circuit 12. When receiving a down signal (d), a down signal receiving circuit 16 separates it into a clock signal (f), a control signal (e), and a synchronizing signal (h) and supplies them to a serial-parallel converting circuit 17. The clock signal (f) and the synchronizing signal (h) extracted by the down signal receiving circuit 16 are always supplied to a parallel-serial converting circuit 19 for up signal, and an up control signal is subjected to time division multiplexing to become a control signal (i), and this signal (i) is converted to a unipolar control signal (k) by an up signal receiving circuit 24 and is converted to a parallel signal by a serial-parallel converting circuit 25.

Synthesis of a T-Carrier Bit Stream Processing System: An Integrated Transmission and Switching System

Abstract: T-carrier is a point-to-point digital time division multiplex transmission system. It is designed to transmit voice and signaling information with low distortion between two points. T-carrier systems are not required to interpret dialed numbers or make routing decisions. When these switching functions are required, the previous approach has been to demodulate the multiplexed signals into their original analog form to be compatible with analog switching entities. However, it is desirable to provide such switching functions while avoiding the demodulation process. This paper describes the synthesis of a T-carrier bit stream processing system which provides transmission and switching functions without the need for time division multiplex demodulation. The resulting system meets telephone company transmission and switching needs in rural communities. First operational service began on March 26, 1976.